Creation of Environmental-benign polymer composites

由于脂肪链的结构和取向，生物可降解聚合物不具有高的力学性能，如强度和弹性模量，因此不能取代高性能塑料。生物降解塑料与增强体的复合材料弥补了这一问题，因此，既要有高的力学性能，又要有良好的生物降解性的增强体是必需的。聚乙醇酸(PGA)晶须的制备一直是我们关注的问题。聚合物是在多相(液-固)溶液聚合中合成的，在该聚合过程中，过量的固体乙交酯作为缓冲剂在聚合过程中保持很高的乙交酯浓度。因此，聚L-乳酸(PLLA)的立体选择性合成具有重要意义，因为PLLA的性质与其立体规整性密切相关。本文通过开环聚合过程中的结晶反应考察了以部分RAC-丙交酯为原料选择性制备PLLA的方法，为立体选择性聚合提供了一种新的途径。在甲苯和正辛烷(体积比40/60)的混合溶剂中，L丙交酯和D，L丙交酯在80℃下聚合。立体选择性聚合如下进行。一旦聚合开始，形成的均低聚物和共聚低聚物是非对映异构体，因此物理性质变得不同。均相齐聚物在聚合初期优先析出形成晶体，这是因为其在溶剂中的相容性比共聚低聚物低。然后，在低聚物的活性链端选择性地聚合L-丙交酯，同时结晶。D，L-丙交酯通过偏析从晶体上的聚合位除去，最终由部分RAC-丙交酯生成D-乳酸单元较少的PLLA晶体

Biodegradable polymers do not possess the high mechanical properties, such as strength and elastic modulus, due to the aliphatic chain structure and its orientation and thereby they cannot replace high performance plastics. The composite of biodegradable plastics with reinforcement compensate this problem and hereby the reinforcement possessing not only the high mechanical properties but also good biodegradability is necessary. We have paid attention to prepare the whisker of polyglycolic acid (PGA). The polymers were synthesized in the heterogeneous (liquid-solid) solution polymerization in which an excess of solid glycolide coexists as a buffer to keep the very high glycolide concentration during polymerization in which temperature. As a result PGA whiskers were obtained as mixtures with dendrite crystals.The stereoselective synthesis of poly(l-lactic acid) (PLLA) is of great importance because the properties of PLLA are highly related to the stereoregularity. Here, the selective preparation of PLLA from partially rac-lactide is examined by the crystallization during ring-opening polymerization as a novel approach for stereoselective polymerization. Polymerizations of L-lactide and D,L-lactide were carried out at 80℃ in the mixed solvent of toluene and n-octane (40 / 60 by volume). The stereoselective polymerization occurs as follows. Once polymerization is started, homo-oligomer and co-oligomer formed are diastereomeric and thereby the physical properties become different. The homo-oligomers are preferentially precipitated to form the crystals at the early of polymerization due to the lower miscibility into solvent than that of co-oligomer. Thereafter, L-lactide is selectively polymerized at the active chain end of oligomers in the crystals with simultaneous crystallization. D,L-lactide is eliminated from the polymerization site on the crystals by segregation and the PLLA crystals containing less D-lactic acid unit are finally formed from partially rac-lactide